For hundreds of years our observations of Mars were restricted by the vast distance separating Earth from the red planet. About once every two years, at its closest approach (called opposition), Mars passes within about 55 million km of Earth and it is then that we are able to capture pictures of maximum resolution with earth-based telescopes. The Hubble Space Telescope now provides us with excellent views from earth-orbit, but until the launching of probes to Mars to collect and relay data back to Earth, much of what was "known" about Mars was based on fuzzy pictures which showed only large scale planetary features and events.
The earth-based observations of Mars paved the way for spacecraft exploration of the planet. So many questions had been raised about Mars and there were so few answers. Did life exist on Mars in the past or present? Was water present on the planet? If so, what form was it in? What was the atmosphere composed of ? These were some of the questions which captured the imaginations of scientists from many disciplines, and the answers could only be found by direct observation.
Outside of the Earth-Moon system, Mars is the most hospitable body in the solar system for humans and is currently the only real candidate for future human exploration and colonization. Mercury is far too close to the Sun ( radiation and temperature extremes) and has almost no atmosphere, Venus is far too hot ) and the surface pressures are extreme, the gas giants ( Jupiter, Saturn, Uranus, Neptune ) do not provide a surface on which to land ( at least until the pressure is far too great! ), and Pluto is far too cold and distant. Some of the moons of Jupiter ( eg. Europa ) and Saturn ( eg. Titan ) are interesting targets in the search for life elsewhere in the solar system, but they are much farther away and far more inhospitable than Mars.
Mars Pathfinder was launched on December 4, 1996 at Cape Canaveral in United States and he reached Mars on July 4, 1997. The mission consists of a stationary lander and a surface rover. The landing site in the Ares Vallis region has been named the Carl Sagan Memorial Station. The Mars Pathfinder was designed primarily to demonstrate a low-cost way of delivering a set of science instruments and a free-ranging rover to the surface of the red planet. Landers and rovers of the future will share the heritage of spacecraft designs and technologies first tested in this "pathfinding" mission.
The scientific objectives include atmospheric entry science, long-range and close-up surface imaging, rock and soil composition and material properties experiments, and meteorology, with the general objective being to characterize the Martian environment for further exploration. Since its landing on July 4, 1997, Mars Pathfinder has returned more than 16,000 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and extensive data on winds and other weather factors. The Mars Pathfinder mission cost approximately $265 million including launch and operations. Development and construction of the lander cost $150 million and the rover about $25 million. The lander and rover operated until communication was lost for unknown reasons on 27 September 1997.